The first fruit of Jacobs' work was the natural laminar flow airfoil. (Natural, in this context, means that no powered method, such as boundary-layer suction, is used to maintain laminar flow.) His work was based on the knowledge that the behavior of the boundary layer -- the thin layer of air, close to the airfoil surface, that the airplane drags along with it -- is influenced by the pressure distribution. A laminar boundary layer, in which all air particles follow paths parallel to the airfoil surface, could be sustained along the front of an airfoil, as its upper and lower surfaces grew farther apart. But when the surfaces began to converge, tiny turbulent eddies and vortices would appear in the boundary layer. The drag of a laminar boundary layer is much less than that of a turbulent one. All airfoils have some laminar flow, but the new family of laminar profiles developed by the NACA extended the laminar boundary layer to as much as 60 percent of the airfoil's length, reducing drag by as much as two-thirds.